1. Field of the Invention
This invention relates generally to intervertebral spinal surgery, and more particularly to surgical instrumentation and to a method for creating one or more spaces between adjacent vertebral bodies in which the space has a shape and vertebral surfaces adapted in size to receive an implant or implants to be implanted in the space, and the method of implanting those implants.
2. Description of the Prior Art
The spinal disc that resides between adjacent vertebral bodies maintains the spacing between those vertebral bodies and, in a healthy spine, allows for relative motion between the vertebrae. With disease and/or degeneration a disc may become painful and/or mechanically insufficient warranting surgical fusion across the affected disc. Where fusion is intended to occur between adjacent vertebral bodies of a patient's spine, the surgeon typically prepares an opening at the site of the intended fusion by removing some or all of the disc material that exists between the adjacent vertebral bodies to be fused. Because the outermost layers of bone of the vertebral endplate are relatively inert to new bone growth, the surgeon must work on the endplate to remove at least the outermost cell layers of bone to gain access to the blood-rich, vascular bone tissue within the vertebral body. In this manner, the vertebrae are prepared in a way that encourages new bone to grow onto or through an implant that is placed between the vertebrae. An implant or insert may or may not promote fusion of the adjacent vertebral bodies, may be an artificial spinal disc, may permit surface ingrowth, and may be made of bone or inert material, such as titanium. All of these examples and more are implants.
Present methods of forming this space between adjacent vertebrae generally include the use of one or more of the following: hand held biting and grasping instruments known as rongeurs; drills and drill guides; rotating burrs driven by a motor; and osteotomes, chisels, and scraping implements. Surgeons often prefer a drilling technique due to its being ease, quick, and accurate. Sometimes the vertebral endplate must be sacrificed as occurs when a drill is used to drill across the disc space and deeper into the vertebrae than the thickness of the endplate. Such a surgical procedure is typically used to prepare a space in the spine for an implant having a circular cross section and necessarily results in the loss of the hardest and strongest bone tissue of the vertebrae, the endplate, and thereby robs the vertebrae of that portion of its structure best suited to absorbing and supporting the loads placed on the spine by everyday activity. Where the surgeon chooses to forego drilling a large bore across the disc space in an attempt to preserve that good bone he must nevertheless use one of the above instruments to work upon the endplates of the adjacent vertebrae to access the vascular, cancellous bone that is capable of participating in the fusion and causing active bone growth, and also to attempt to obtain an appropriately shaped surface in the vertebral bodies to receive the implant, which means and method are unreliable for that purpose.
There exists therefore a need for an improved surgical instrumentation and a related method for providing a space that is non-circular in cross section, and preferably a substantially quadrilateral space across the height of a disc space and into the adjacent surfaces of the adjacent vertebral bodies while taking advantage of the safe, easy, and accurate technique of boring or drilling into the spine to form a space and to shape the adjacent endplates to receive implants not typically associated with boring techniques.